1. Field of the Invention
The present invention relates to a pulse width modulation controller, and more specifically to a digital pulse width modulation controller, which dynamically changes the resolution of the duty of the current pulse width modulation signal based on the change state of the duty of the previous pulse width modulation signal.
2. The Prior Arts
In the prior arts, the technology of pulse width modulation (PWM) is primarily used to modulate the pulse signal with specific frequency to generate the corresponding PWM signal by changing the width of the pulse according to specific conditions. The PWM signal then drives switching elements for electric devices or loading circuits, such as light emitting diodes (LEDs), electric motors or power converters. In general, the minimum adjustable unit of the pulse width is referred as “resolution”. For instance, the resolution of the pulse signal with the frequency of 100 KHz is 1/100K second.
As for the application of driving two switching elements, the PWM technology have to generate two corresponding PWM signals, each having the same width/frequency and reversed polarity, that is, one PWM signal is high/low level when another PWM signal is low/high level, so as to avoid turning on or conducting the two switching elements at the same time, which may cause extremely large current to flow through the loading circuit and even lead to short-circuiting with permanent damage.
To achieve the above function, the traditional means is implemented by the analog or digital circuits with the feedback control loop. For the analog solution, the PWM frequency is generated by the built-in oscillator, and it is not possible to freely change the PWM frequency according to the actual situation. In particular, the compensation of the internal amplifier commonly used in the conventional feedback control loop is not adjustable. In addition, it is not easy to change the output voltage and the loading range, which are usually preset.
For the current digital solution with digital power function, the analog feedback signal generated by fast sampling operation provided with the analog-to-digital converter (ADC) is required and then is controlled by the digital signal processing (DSP) engine, such as Proportional-Integral-Derivative (PID) control. However, higher resolution needs faster operating frequency, and at the same time, the sampling frequency of the ADC has to be higher enough. As a result, the above digital solution results in higher cost, and is not feasible for most of the actual applications.
Moreover, the conventional solutions can not dynamically change the interval when the two pulse signals are specified to low level at the same time to improve the electric performance of the loading, like the average power consumption.
Therefore, it is urgently needed to provide a digital pulse width modulation controller, which can dynamically adjust the resolution of the duty of the current PWM signal to overcome the above problems in the prior arts.